Power switch device and method for cluster computer

ABSTRACT

A power switch device and method for a cluster computer is described. A power input circuit receives plural input powers and plural state signals corresponding to the input powers. A first output circuit supplies the input powers to a head node and at least one compute node. A second output circuit supplies the input powers to the head node. A gate produces a switch signal according to the state signals. According to the switch signal, a switch module connects the power input circuit to the first output circuit or the second output circuit. And a spare power module, connected to the first and second output circuits, stores a spare power charged from the first output circuit and supplies the spare power to the second output circuit during a switch period.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a device and method for electricityswitching, and more particularly, to a power switch device and methodfor a cluster computer.

2. Related Art

Stable power source is one of the most significant considerations to acomputer system, especially to those applied to the field of highperformance computing (HPC). Currently, to provide electricity steadilyand avoid unexpected shutdown, a super computer with hundreds of nodesutilizes a large UPS (uninterrupted power system, UPS) as an externalAC-to-AC power supply system. However, the external UPS is not capableof solving any power supply problems happening inside the computersystem.

Except the external power supply system, an internal AC (alternatingcurrent)-to-DC (direct current) RPS (redundant power system) also keepsthe computer system operating without interruptions. The primaryfeatures of a RPS are at-least-two power suppliers and hot-swap support.Therefore, when any of the operating power suppliers is failed ordisconnected, the computer system will remain operative; which meanseach of the power suppliers in a RPS has to be capable of independentlysupplying all the electricity required by the computer system.Accordingly, the power supplier applied in a RPS supplies higher power,along with larger volume and high cost.

However, for low-nodes cluster computer, the internal RPS is notperfectly applicable. Please refer to FIG. 1, which illustrates apersonal super computer (PSC) for personalized HPC that has applicationsin small-scale computing fields such as graphic processing, modelanalysis and research simulation. In FIG. 1 the PSC includes five motherboards; one operates as a head node 80, while the rest four areperformed as compute nodes 82. A first power supplier 70 and a secondpower supplier 71 supply and distribute electricity through a powerdistribution circuit 90 to the head node 80 and the four compute nodes82. However, PSC is a performance-oriented, density-oriented andcost-oriented product. If the first power supplier 70 and the secondpower supplier 71 are designed according to the system architecture ofRPS, the problems of space distribution and cost will come along.Oppositely, if the RPS architecture is not utilized, the reliabilitywill go down.

For example, each of the first and second power suppliers 70 and 71provides 850 W, total 1700 W of electricity. Each of the compute nodes82 needs 280 W, while the head node 80 needs 450 W; the whole systemwill then need 1570 W. When the first supplier 70 fails suddenly, thewhole system will lost 850 W electricity in an extremely short time. Ifthe whole system still shares the remaining 850 W electricity, then thepower left for each node will be 170 W, which is obviously too much blowthe required power for each node. That will cause the computer system anabnormal shutdown with irrecoverable data damage and serious taskinterruptions. At the moment, even the external UPS still provides withAC as usual, DC spare power is not available.

That proves that the power supplier in the prior art exists acontradiction between space distribution, cost control and reliability.Therefore, the issue becomes critical about how to improve thearchitecture of the power supply system in the prior art, providing thesame power with a downsized volume and lower cost, and securing the dataduring the sudden power-off or abnormal shutdown duration.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a power switch device andmethod for cluster computer.

The power switch device for cluster computer according to the presentinvention includes a power input circuit, a first output circuit, asecond output circuit, a gate, a switch module and the spare powermodule.

The power input circuit receives input powers and state signalscorresponsive to the input power from power suppliers. The gategenerates a switch signal according to the state signal, while theswitch module electrically connects the power input circuit to one ofthe first output circuit and the second output circuit according to theswitch signal.

When all the state signals indicate all the input power are in apower-on state, the switch module electrically connects to the firstoutput circuit, by which outputting the input powers to the head nodeand the compute nodes. On the other hand, when at least one of the statesignals indicates that at least one of the input powers fails, theswitch module electrically connects to the second output circuit, bywhich outputting the remaining input power to the head node.

The spare power module electrically connects to the first output circuitand the second output circuit, charging and storing a spare powerthrough the first output circuit. During a switch period of the switchmodule, the spare power module provides the stored spare power to thesecond output circuit.

The power switch method according to the present invention is applied toa first output circuit and a second output circuit of a clustercomputer. The first output circuit supplies electricity to a head nodeand at least one compute node, while the second output circuit supplieselectricity to the head node. The method includes the following steps:receiving plural input powers and plural state signals corresponsive tothe input powers; confirming according to the state signals whether anyof the input powers is in a power-off state; switching the remaininginput power from the first output circuit to the second output circuit;providing a spare power through the second output circuit to the headnode during a switch period of said switching step; and supplying theremaining input power to the head node through the second outputcircuit.

Consequently, the power switch device and method according to thepresent invention provides high density, low cost and high reliability.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow illustration only, and thus arenot limitative of the present invention, and wherein:

FIG. 1 shows a cluster computer and its internal spare power system inthe prior art.

FIG. 2 shows the first embodiment of a power switch device for clustercomputer according to the present invention.

FIG. 3 shows the second embodiment of a power switch device for clustercomputer according to the present invention.

FIG. 4 is a flow chart of a power switch method for cluster computeraccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Please refer to FIG. 2, which illustrates the first embodiment of apower switch device for a cluster computer according to the presentinvention.

A cluster computer 08 includes a head node 80 and compute nodes 82. Thehead node 80 and the compute nodes 82 may be computer systems of singleor multiple processors configured on five individual mainboards. Thehead node 80 manages the four compute nodes 82 to perform the tasks ofcluster computing. The electricity required by the cluster computer 08is provided by a the first power supplier 70 and a second power supplier72. A power switch 01 is utilized to transform voltages, distributeelectricity and switch between different power-supply mechanisms.

Generally, in the embodiment the first power supplier 70 and the secondpower supplier 72 has to supply electricity together to all the powerloads of the head node 80 and all the compute nodes 82. Namely, neitherthe first power supplier 70 nor the second power supplier 72 can supplyenough electricity to the whole cluster computer 08 independently.

The power supply device 01 includes a power input circuit 10, a firstoutput circuit 20, a second output circuit 30, a gate 40, a switchmodule 50 and the spare power module 60.

The power input circuit 10 electrically connects the first powersupplier 70, the second power supplier 72, the gate 40 and the switchmodule 50. As to power distribution, the power input circuit 10 receivesinput powers P1 and P2 (provided by the first power supplier 70 and thesecond power supplier 72), and transmit to the switch module 50. Statesignals S1 (such as PSON1_L) and S2 (such as PSON2_L) corresponsive tothe input powers P1, P2 are transmitted to the gate 40 respectively.

The gate 40, in circuit connection with the first power supplier 70, thesecond power supplier 72 and the switch module 50, generates a switchsignal Sw according to the state signals S1, S2 of the input powers P1,P2, and transmits to the switch module 50.

The switch module 50 is in circuit connection with the first powersupplier 70, the second power supplier 72 and the gate 40. In thepresent embodiment, the switch module 50 is predetermined to be incircuit connection with the first output circuit 20. The switch modulereceives the switch signal Sw of the gate 40 to remain the power inputcircuit 10 connecting electrically with the first output circuit 20, orto switch for connecting with the second output circuit 30.

The first output circuit 20 electrically connects with the switch module50, the head node 80 and each of the compute nodes 82, to output theinput powers P1, P2 together and distribute to the head node 80 and eachof the compute nodes 82. The second output circuit 30 electricallyconnects to the switch module 50, the head node 80 and the spare powermodule 60, to output the remaining input power P1 or P2, or the sparepower Ps of the spare power module 60 to the head node 80.

The spare power module 60, electrically connecting to the first outputcircuit 20 and the second output circuit 30, is charged by the firstoutput circuit 20 to store a spare power Ps. The spare power Ps issupplied to the head node 80 through the second output circuit 30 duringa switch period of the switch module 50. The spare power module 60 mayinclude various types of capacitors (including ultra-capacitor) ormodules thereof, which has enough capacitance to independently supplythe electricity required by the head node 80 for a short specificduration (longer than the switch period).

The switch 55 located between the first output circuit 20 and the sparepower module 60 is used for limiting the direction of the current, whichmay be realized by a MOS switch or a diode switch. As long as thealgorism of power supply is designated to provide electricity only tothe head node 80 while the input power P1 or P2 fails, the switch 55will allow the spare power module 60 to be charged by the first outputcircuit 20, and prevent from discharging to the first output circuit 20and the four compute nodes 82 during the switch period. Therefore, thespare power module 60 only needs to supply less power (only for the headnode 80). However, in another case, if the spare power module 60 isdesigned to discharge to the first output circuit 20 and the fourcompute nodes 82, the switch 55 will not be necessary any more; only thespare power module 60 will need to supply more power load that is closeto the sum of the power loads of the two power suppliers 70, 72.

When both the input powers P1, P2 are in a power-on state, thecorresponsive state signals S1, S2 will be in a specific power-on logiclevel of the supplied voltage (such as PSON1_L (S1), PSON2_L (S2) underlogic LOW) to allow the switch signal Sw generated by the gate 40 tocontrol the switch module 50 to maintain the electrical connection withthe first output circuit 20. When one of the input powers P1, P2 is inpower-off state, the corresponsive state signals S1, S2 will be in aspecific power-off logic level of the supplied voltage (such as PSON1_L(S1), PSON2_L (S2) under logic HIGH) to allow the switch signal Swgenerated by the gate 40 to control the switch module 50 to switch tothe electrical connection with the second output circuit 30. To achievethe switch controls as mentioned above, the gate 40 may be an AND logicgate, while the switch module 50 may be a relay.

For the power supply device 01 disclosed in the present invention, whenboth of the state signals S1, S2 indicate the input powers P1, P2 are inthe power-on state, the switch module 50 will keep the power inputcircuit 10 electrically connecting to the first output circuit 20.Meanwhile, through the first output circuit 20, both the input powersP1, P2 will be output to the head node 80 and each of the compute nodes82. At the moment, the spare power module 60 will be charged and storingthe spare power through the first output circuit 20.

When the state signals S1, S2 indicate any of the input powers P1, P2fails, the switch module 50 will switch the power input circuit 10 toelectrically connect to the second output circuit 30. At the moment, theremaining input power P1 or P2 can not independently fulfill theelectricity demand of the head node 80 and all of the compute nodes 82.Consequently, the switch module 50 will switch the power input circuit10 to electrically connect to the second output circuit 30, therebyoutputting the remaining input power P1 or P2 to the head node 80through the second output circuit 30.

Generally during the switch period, the switch module 50 needs severalmilliseconds for switch operation, so without connecting with the powerinput circuit 10 the first output circuit 20 and the second outputcircuit 30 will not be supplied with electricity in milliseconds. Inaddition, at the initial stage the power supply state is still unstable.Then, the spare power Ps provided by the spare power module 60 will beoutput to the head node 80 through the second output circuit 30 tomaintain normal power supply for the head node 80. Therefore the headnode 80 will be able to process the task interruptions of each of thecompute nodes 82, and to store the final operating data of the computenodes 82 that are sent back before the compute nodes 82 shut down. Thatis why the spare power module 60 in the present invention needs to becapable of independently supplying the electricity required by the headnode 80 during the specific duration.

Besides, about the selection on power suppliers, the sum of the outputpowers of the aforesaid first and second power suppliers 70, 72 equalsto the sum of the output powers required by the head node 80 and all thecompute nodes 82 plus a safe value.

For example, as shown in FIG. 2, the head node 80 needs 450 W power,while each of the four compute nodes 82 needs 280 W power; the wholesystem will need 1570 W power. By way of using the power supply device01 of the cluster computer 08 according to the present invention, eachof the first power supplier 70 and the second power supplier 72 needsonly to provide about 850 W power, with a safe value of 130 W power.Thus, the reliability of the whole power supply system may bemaintained; unlike the RPS (redundant power system) in the prior artthat each power supplier needs to provide 1570 W power, along withhigher cost and space configuration problems.

Please refer to FIG. 3, which illustrates the second embodiment of thepower supply device for cluster computer. Practically, all the nodes ofthe cluster computer would possibly need several different operationvoltages for various components. Thus, the spare power module will needto provide the spare power with different voltages, and the DC-DCvoltage distribution capability also needs to be fulfilled.

Accordingly, the major differences between the present embodiment andthe former one, is that the power supply device 01 of the presentinvention further includes a DC (direct current) voltage distributioncircuit 14, a first distribution circuit 22 and a second distributioncircuit 32 to distribution the input powers P1, P2 into three voltagesV1, V2, V3 for each nodes. Three switch modules 51, 52, 53 for thevoltages V1, V2, V3 and three spare power modules 61, 62, 63, are alsoincluded to enable the circuit switch control for the different voltagesV1, V2, V3 and to supply three different spare powers Ps1, Ps2 and Ps3.

Except connecting with the gate 40, the first power supplier 70 and thesecond power supplier 72, the power input circuit 10 is also in circuitconnection with the three switch modules 51, 52, 53. The power inputcircuit 10 includes input connection units 12, 13 and the DC voltagedistribution circuit 14.

The input connection units 12, 13 are power connectors, receiving theinput powers P1, P2 and the state signals S1, S2 provided by the firstpower supplier 70 and the second power supplier 72.

The DC voltage distribution circuit 14, electrically connecting to theinput connection units 12, 13, distributes the input powers P1, P2 intothe different voltages V1, V2, V3 (such as 3.3V, 5V, 12V), and thentransmits to the switch modules 51, 52, 53. For those skilled in theart, the DC voltage distribution circuit 14 may be integrated in thefirst power supplier 70 and the second power supplier 72, only needs toprovide dedicated power connectors for different voltages. Therefore,the DC voltage distribution circuit 14 is not absolutely essential forthe power supply device 01 to implement thereon.

The first output circuit 20 includes the first distribution circuit 22and the first output connection units 241, 242, 243. The firstdistribution circuit 22 is to electrically connect with the switchmodules 51, 52, 53 and the spare power modules 61, 62, 63, to receivethe input powers that the DC voltage distribution circuit 14 transmitsto the switch modules 51, 52, 53.

The first output connection units 241, 242, 243, including plural powerconnectors with different voltages, electrically connect the firstdistribution circuit 22, the head node 80 and the four compute nodes 82,to output the input powers to the head node 80 and all of the computenodes 82.

The second output circuit 30 includes the second distribution circuit 32and the second output connection units 341, 342, 343. The seconddistribution circuit 32 electrically connects the switch modules 51, 52,53 and the spare power modules 61, 62, 63, to receive the input powerstransmitted from the DC voltage distribution circuit 14 to the switchmodules 51, 52, 53.

The second output connection units 341, 342, 343, including plural powerconnectors of different voltages, electrically connects the seconddistribution circuit 32 and the head node 80 to output the remaininginput power to the head node 80.

The switch modules 51, 52, 53 switch according to the switch signal ofthe gate 40 and for different voltages respectively, to keep the powerinput circuit 10 electrically connecting to the first output circuit 20,or to switch to the second output circuit 30.

The spare power modules 61, 62, 63, electrically connecting to thedifferent voltages portions V1, V2, V3 of the first output circuit 20and the second output circuit 30, are charged by the first outputcircuit 20 in accordance with dedicated voltages to store the sparepowers Ps1, Ps2, Ps3. During the switch periods of the switch modules51, 52, 53, the spare powers Ps1, Ps2, Ps3 are provided to the secondoutput circuit 30.

Take the power supply mechanism of voltage V1 as an example. The inputpowers P1 and P2 provided by the first power supplier 70 and the secondpower supplier 72 are received through the input connection units 12,13, and then distributed by the DC voltage distribution circuit 14 intodifferent voltages V1, V2 and V3 for each node. When both the statesignals S1, S2 indicate the input powers P1, P2 are in the power-onstate, the switch module 51 will keep the voltage V1 part of the powerinput circuit 10 electrically connecting to the voltage V1 part of thefirst output circuit 20. Therefore, the distributed input power (voltageV1) will be transmitted through the switch module 51, the firstdistribution circuit 22, to the first output connection unit 241, andwill eventually arrive the head node 80 and the compute nodes 82.Meanwhile, the spare power module 61 is charged and storing the sparepower as well.

When the state signals S1, S2 indicate any of the input powers P1, P2 isin the power-off state, the switch module 51 will switch the voltage V1part of the power input circuit 10 to electrically connect to the secondoutput circuit 30. At the moment since a part of the input powers areinterrupted, the remaining input power can not independently fulfill theelectricity requirement of the head node 80 and all the four computenodes 82. Accordingly, the second distribution circuit 32 has totransmit the remaining input power of voltage V1 through the secondoutput connection unit 34 to the head node 80.

During the switch period of the switch module 50, without the connectionof the first output circuit 20 and the second output circuit 30 to thepower input circuit 10, there will be several milliseconds that thewhole system is in the power-off state. Then the spare power Ps1(voltage V1) provided by the spare power module 61 will be transmittedthrough the second output circuit 30 to the head node 80, therebymaintain the normal power supply condition of the voltage V1 part of thehead node 80.

The power supply device of the present invention may be practicallyconfigured on a power switch board, without the spare power moduledisclosed in the former embodiments limited thereon. On a premise thatthe circuit connections of the spare power module according to thepresent invention are not changes, the spare power module may beconfigured on the head node, or implemented outside the head node or thepower switch board independently.

Furthermore, the switch signal Sw may be transmitted to some GPIO(general purpose input/output) pin of some specific controller on thehead node 80 as a signal or command source for the operating system ofthe cluster computer to process interruption tasks. As to the switch 55applied in FIG. 2, it can be configured between the first output circuit20 and the spare power module 60 in FIG. 3 by demand.

Please refer to FIG. 4, which illustrates a flow chart of a power switchmethod for cluster computer. According to the power supply devicedisclosed in the former embodiment, the power switch method of thepresent invention basically related to a power supply mechanism for ahead node and plural compute nodes of the cluster computer when any ofthe power suppliers is under the power-off state. The method includesthe following steps.

Step 110: First, receive the input powers (P1, P2 . . . ) and thecorresponsive state signals (S1, S2 . . . ). Each of the state signalsis provided to indicate whether the input powers are in the power-onstate or the power-off state, and also to be integrated by the switchmodule to generate the switch signals. Meanwhile, the sum of the outputpowers of the input powers equals to the sum of the overall operationpowers of the whole cluster computer (the head node and all the computenodes) plus a safe value. In another word, any of the input powers isnot capable of independently supplying the overall electricityrequirement of the whole cluster computer.

Step 120: Confirm according to the state signal whether any of the inputpowers is in the power-off state. The state signals may be used todecide whether each of the input powers is supplied normally. If all theinput powers are in the power-on state, their corresponsive state signalwill be in a specific logic voltage level of the power-on operation(such as the signal PWRON_L under logic LOW), and then the system willgo back to the step 110 to continuously receive the following inputpowers and the state signals. Meanwhile, the output power will be keptinputting to the first output circuit. Oppositely, if any of the inputpower is in the power-off state, its corresponsive state signal will bein a specific logic voltage level of the power-off operation (such asthe signal PWRON_L under logic HIGH), thereby generating the switchsignal Sw to proceed the switch operation of the power supplymechanisms. Between the steps 120 and 130, a step of generating theswitch signal according to the state signals may be further included.

Step 130: When any of the input power is in the power-off state, theremaining input power will not be able to independently supply theoverall electricity requirements of the whole cluster computer. Hencethe remaining input power should be switched from the first outputcircuit that serves the whole cluster computer, to the second outputcircuit that serves the head node only. That switch operation has to beperformed according to the switch signal.

Step 140: Since the switch module needs the switch period of saidswitching step 130 to switch from the first output circuit to the secondoutput circuit, the spare power (Sw) will be provided through the secondoutput circuit to the head node. To avoid the spare power being providedto the first output circuit, the supplied subject that the spare poweris provided to may be limited. Namely, a step of preventing the sparepower from supplying to the first output circuit may be furtherincluded.

Step 150: When the switch module has switched the remaining input powerfrom the first output circuit to the second output circuit, theremaining input power will be able to provide to the head node.

In the aforesaid embodiment, the cluster computer takes the first outputcircuit as the predetermined power supply path. Therefore the powerswitch method of the present invention further includes a step ofcharging a spare power module by the first output circuit for storingthe spare power when all the input powers are in the power-on state.When any of the input power is in the power-off state, the system willbe switch to use the second output circuit to supply electricity to thehead node, while during the switch period the spare power module willserve the head node. Additionally, the second output circuit will becapable of charging the spare power module after the switch operation.

In the condition that the second output circuit serves the head nodewith all of the compute node shut-down, if the interrupted powersupplier is replaced and back in service (all the input powers return tothe power-on state), then the switch module is possibly to be switchedaccording to the state signal back to the first output circuit forserving the whole cluster computer. Provided with enough capacitance,during the switch period of switching from the second output circuitback to the first output circuit, the head node may possibly be servedby the spare power module.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A power switch device for a cluster computer, comprising: a powerinput circuit, receiving a plurality of input powers and a plurality ofstate signals corresponsive to the input powers respectively; a firstoutput circuit, supplying electricity to a head node and at least onecompute node of the cluster computer; a second output circuit, supplyingelectricity to the head node; a gate, generating a switch signalaccording to the state signals; at least one switch module, electricallyconnecting the power input circuit to one of the first output circuitand the second output circuit according to the switch signal; and atleast one spare power module, electrically connecting to the firstoutput circuit and the second output circuit, the spare power modulebeing charged through the first output circuit and storing a sparepower, the spare power being provided to the second output circuitduring a switch period of the switch module.
 2. The power switch deviceof claim 1, wherein the input powers and the state signals are providedby a plurality of power suppliers.
 3. The power switch device of claim2, wherein the sum of the output powers of the power suppliers equals tothe sum of the output powers required by the head node and the computenode plus a safe value.
 4. The power switch device of claim 1, whereinthe spare power module comprises at least one capacitor.
 5. The powerswitch device of claim 1, further comprising a switch connected betweenthe first output circuit and the spare power module to limit the currentdirection thereof.
 6. The power switch device of claim 1, wherein theswitch module comprises a relay.
 7. The power switch device of claim 1,wherein the power switch device is configured on a power switch circuitboard.
 8. The power switch device of claim 7, wherein the spare powermodule is configured on the head node, or independently configuredoutside the head node and the power switch circuit board.
 9. The powerswitch device of claim 1, wherein the gate comprises an AND logic gate.10. The power switch device of claim 1, wherein the power input circuitcomprises a plurality of input connection units for receiving the inputpowers and the state signals.
 11. The power switch device of claim 10,wherein the power input circuit comprises a DC (direct current) voltagedistribution circuit electrically connecting to the input connectionunits to divide the input powers into various DC voltages and transmitto the switch module.
 12. The power switch device of claim 1, whereinthe first output circuit comprises; a first distribution circuit,electrically connecting the switch module and the spare power module;and at least one first output connection unit, electrically connectingthe first distribution circuit, the head node and the compute node. 13.The power switch device of claim 1, wherein the second output circuitcomprises; a second distribution circuit, electrically connecting theswitch module and the spare power module; and at least one second outputconnection unit, electrically connecting the second distribution circuitand the head node.
 14. A power switch method applying to a first outputcircuit and a second output circuit of a cluster computer, the firstoutput circuit supplying electricity to a head node and at least onecompute node of the cluster computer, the second output circuit supplyelectricity to the head node, the method comprising the steps of;receiving a plurality of input powers and a plurality of state signalscorresponsive to the input powers; confirming according to the statesignals whether any of the input powers is in a power-off state;switching the remaining input power from the first output circuit to thesecond output circuit; providing a spare power through the second outputcircuit to the head node during a switch period of said switching step;and supplying the remaining input power to the, head node through thesecond output circuit.
 15. The method of claim 14, wherein the inputpowers are input to the first output circuit when all the state signalsindicate all the input powers are in a power-on state.
 16. The method ofclaim 15 further comprising a step of charging a spare power module bythe first output circuit for storing the spare power when all the inputpowers are in the power-on state.
 17. The method of claim 14, whereinthe step of confirming according to the state signals whether at leastone of the input powers is in the power-off state, further comprises astep of generating a switch signal according to the state signals. 18.The method of claim 17, wherein the remaining input power is switchedfrom the first output circuit to the second output circuit according tothe switch signal.
 19. The method of claim 14 further comprising a stepof preventing the spare power from supplying to the first outputcircuit.